A man walks with speed 15 km/hr instead of 12 km/hr and covers 20 km more distance. Find the distance covered by him with speed 15 km/hr.

Considering the time period to be equal ,
Walking with a speed of 12 km/hr , x km is covered.
Walking with a speed of 15 km/hr , x+ 20 km is covered.
Since time period is equal,
x/12 = (x+20)/15
15x = 12x + 240
15x - 12x = 240 
3x = 240
x = 80 km
Hence the distance covered by the man with a speed of 15 km/hr is 80+20= 100 km